1. Field of the Invention
This invention relates generally to high speed rod rolling mills, and is concerned in particular with improvements in the laying heads used to form the hot rolled products of such mills into helical ring formations for deposit on cooling conveyors and the like.
2. Description of the Prior Art
A conventional laying head is depicted in FIG. 1 at 10. The laying head has a housing 12 and a quill 14 supported between first and second bearing assemblies 16, 18 for rotation about its axis "X". The centers of the bearings 16, 18 lie in respective reference planes P.sub.1, P.sub.2 spaced one from the other by a distance "B". The second bearing assembly 18 has a bore diameter "D".
Quill 14 carries a bevel gear 20 meshing with a larger diameter bevel gear 22, the latter being driven by conventional means (not shown). A laying pipe 24 is carried by the quill for rotation therewith. The laying pipe has an entry section 24.sub.a lying on the quill axis X between the first and second bearing assemblies 16, 18, and a three dimensionally curved intermediate section 24.sub.b leading from the entry section across reference plane P.sub.2 to a delivery end 24.sub.c. The delivery end is spaced from reference plane P.sub.2 by an overhang distance "A", and is spaced radially from axis X to define a circular path of travel having a diameter "F". The laying pipe is held by a pipe support structure 26 comprising arms extending radially from the quill. Hot rolled product is directed into the entry section 24.sub.a of the laying pipe, and emerges from the delivery end 24.sub.c as a continuous helical formation of rings having diameters F.
With reference to FIG. 2, it will be seen that under static conditions, the rotating assembly comprising the quill, laying pipe and support structure deflects under its own weight "W" as indicated diagrammatically by the curve 28 (exaggerated for purposes of illustration). Thus, the centroid 30 of the rotating assembly will depart laterally from the axis of rotation X by a distance "Y". The extent to which lateral centroid deflection Y is minimized is considered to be a measure of the "stiffness" of the laying head.
It is generally accepted that a safe operating speed for a laying head is not more than about 65% of the critical resonance speed of the rotating assembly. Critical resonance speed varies inversely as the square root of the lateral deflection Y.
Laying heads are currently operating satisfactorily at mill delivery speeds on the order of 100-110 m/sec. However, as these speeds continue to increase to 120 m/sec and higher, the ability of conventional laying heads to function satisfactorily at these elevated speeds is projected to become increasingly problematical. The reason appears to be inadequate stiffness, which not only lowers the critical resonance speed of the rotating assembly, but also leads to the introduction of unacceptably pronounced vibrations.
The objective of the present invention is to achieve a marked increase in stiffness of laying heads, thereby overcoming the problems associated with the prior art and making it possible to meet the ever increasing speed demands of modern high speed mills.